Information storage devices are used to retrieve and/or store data in computers and other consumer electronics devices. A magnetic hard disk drive is an example of an information storage device that includes one or more heads that can both read and write, but other information storage devices also include heads—sometimes including heads that cannot write. For example, in an optical disk drive, the head will typically include a mirror and objective lens for reflecting and focusing a laser beam on to a surface of the disk.
In a modern magnetic hard disk drive device, each head is a sub-component of a head gimbal assembly (HGA) that typically includes a suspension assembly with a laminated flexure to carry the electrical signals to and from the head. The HGA, in turn, is a sub-component of a head stack assembly (HSA) that typically includes a plurality of HGAs, an actuator, and a flexible printed circuit (FPC) that includes a flex cable. The plurality of HGAs are attached to various arms of the actuator, and each of the laminated flexures of the HGAs has a flexure tail that is electrically connected to the FPC of the HSA.
In many disk drives, the actuator includes arms that position the heads, and that extend from an actuator body. The actuator body includes a bore into which a pivot bearing is fixed by a tolerance ring. Typically, tolerance rings include a cylindrical base portion and a plurality of contacting portions that are raised or recessed from the cylindrical base portion. The contacting portions are typically partially compressed during installation to create a radial preload between the mating cylindrical features of the parts joined by the tolerance ring. The radial preload compression provides frictional engagement that prevents axial slippage of the mating parts. For example, in disk drive applications, the radial compressive preload of the tolerance ring prevents separation and slippage at the interface between the actuator body and the pivot bearing during operation and during mechanical shock events. The tolerance ring also acts as a radial spring. In this way, the tolerance ring positions the interior cylindrical part relative to the exterior cylindrical part while making up for radial clearance and manufacturing variations in the radius of the parts.
The rotational position of the actuator body and arms about the pivot bearing may be changed and controlled, by a magnetic interaction between fixed magnets and an electromagnetic coil that extends from the actuator body in a direction that is generally opposite from the actuator arms. However, the protruding arms and coil may participate in mechanical resonances of the actuator, in a way somewhat reminiscent of a tuning fork. The actuator body may also participate in such a resonance by rocking against or about its attachment constraints.
Such actuator resonances may be excited by intentional rotational accelerations of the actuator about the pivot bearing and/or unintentional rotational or translational mechanical shocks to the actuator structure or its attachment. Any mechanical resonance of the actuator is generally undesirable, and may become problematic if it is characterized by a resonance frequency that is too closely aligned with an excitation and/or a resonance frequency of coupled structure, and/or if its amplitude becomes excessive.
Therefore, there is a need in the art for an improved actuator structure that may better control mechanical resonances of the actuator body and/or a protruding coil or arm.